Crypt::PK::DSA(3) User Contributed Perl Documentation Crypt::PK::DSA(3)
NAME
Crypt::PK::DSA - Public key cryptography based on DSA
SYNOPSIS
### OO interface
my $message = 'hello world';
my $signer = Crypt::PK::DSA->new();
$signer->generate_key(30, 256);
my $signature = $signer->sign_message($message, 'SHA256');
my $public_der = $signer->export_key_der('public');
my $verifier = Crypt::PK::DSA->new(\$public_der);
$verifier->verify_message($signature, $message, 'SHA256') or die "ERROR";
my $ciphertext = $verifier->encrypt("secret message");
my $plaintext = $signer->decrypt($ciphertext);
my $private_der = $signer->export_key_der('private');
my $private_pem = $signer->export_key_pem('private');
my $public_pem = $verifier->export_key_pem('public');
DESCRIPTION
DSA is primarily a digital signature scheme. In this module, signing
and verification are the most common operations and therefore the
primary examples.
Legacy function-style wrappers still exist in code for backwards
compatibility, but they are intentionally undocumented.
METHODS
new
my $source = Crypt::PK::DSA->new();
$source->generate_key(20, 128);
my $public_der = $source->export_key_der('public');
my $pub = Crypt::PK::DSA->new(\$public_der);
my $private_pem = $source->export_key_pem('private', 'secret', 'AES-256-CBC');
my $priv = Crypt::PK::DSA->new(\$private_pem, 'secret');
Passing $filename or "\$buffer" to "new" is equivalent: both forms
immediately import the key material into the new object.
generate_key
Uses the bundled "chacha20" PRNG via libtomcrypt's "rng_make_prng".
Returns the object itself (for chaining).
$pk->generate_key($group_size, $modulus_size);
# $group_size ... [integer] size of the subgroup (q) in bytes; must satisfy: 15 < $group_size < 1024
# $modulus_size .. [integer] size of the prime (p) in bytes; must satisfy: ($modulus_size - $group_size) < 512
# $modulus_size must be >= $group_size
#
# The two-integer form uses Perl's usual numeric-to-integer coercion before
# the XS call. Callers should therefore pass exact integers; values like
# C<10.9> or C<"1e1"> will be coerced according to Perl's integer conversion.
### Common parameter pairs (group_size, modulus_size) => security level:
# generate_key(20, 128) => 80-bit security (1024-bit p, 160-bit q)
# generate_key(30, 256) => 120-bit security (2048-bit p, 240-bit q)
# generate_key(32, 256) => 128-bit security (2048-bit p, 256-bit q)
# generate_key(35, 384) => ~140-bit security (3072-bit p, 280-bit q)
# 140 bits => generate_key(35, 384)
# 160 bits => generate_key(40, 512)
### Sizes according section 4.2 of FIPS 186-4
# (L and N are the bit lengths of p and q respectively)
# L = 1024, N = 160 => generate_key(20, 128)
# L = 2048, N = 224 => generate_key(28, 256)
# L = 2048, N = 256 => generate_key(32, 256)
# L = 3072, N = 256 => generate_key(32, 384)
$pk->generate_key($param_hash)
# $param_hash is { p => $p, q => $q, g => $g }
# where $p, $q, $g are hex strings
$pk->generate_key(\$dsa_param)
# $dsa_param is the content of DER or PEM file with DSA params
# e.g. openssl dsaparam 2048
import_key
Loads private or public key in DER or PEM format.
my $source = Crypt::PK::DSA->new();
$source->generate_key(20, 128);
my $public_der = $source->export_key_der('public');
my $pub = Crypt::PK::DSA->new();
$pub->import_key(\$public_der);
my $private_pem = $source->export_key_pem('private', 'secret', 'AES-256-CBC');
my $priv = Crypt::PK::DSA->new();
$priv->import_key(\$private_pem, 'secret');
The same method also accepts filenames instead of buffers.
Loading private or public keys from a Perl HASH:
$pk->import_key($hashref);
# where $hashref is a key exported via key2hash
$pk->import_key({
p => "AAF839A764E04D80824B79FA1F0496C093...", #prime modulus
q => "D05C4CB45F29D353442F1FEC43A6BE2BE8...", #prime divisor
g => "847E8896D12C9BF18FE283AE7AD58ED7F3...", #generator of a subgroup of order q in GF(p)
x => "6C801901AC74E2DC714D75A9F6969483CF...", #private key, random 0 < x < q
y => "8F7604D77FA62C7539562458A63C7611B7...", #public key, where y = g^x mod p
});
Supported key formats:
o DSA public keys
-----BEGIN PUBLIC KEY-----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-----END PUBLIC KEY-----
o DSA private keys
-----BEGIN DSA PRIVATE KEY-----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-----END DSA PRIVATE KEY-----
o DSA private keys in password protected PEM format:
-----BEGIN DSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-CBC,227ADC3AA0299491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-----END DSA PRIVATE KEY-----
o SSH public DSA keys
ssh-dss AAAAB3NzaC1kc3MAAACBAKU8/avmk...4XOwuEssAVhmwA==
o SSH public DSA keys (RFC-4716 format)
---- BEGIN SSH2 PUBLIC KEY ----
Comment: "1024-bit DSA, converted from OpenSSH"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---- END SSH2 PUBLIC KEY ----
export_key_der
Returns the key as a binary DER-encoded string.
my $private_der = $pk->export_key_der('private');
#or
my $public_der = $pk->export_key_der('public');
export_key_pem
Returns the key as a PEM-encoded string (ASCII).
my $private_pem = $pk->export_key_pem('private');
#or
my $public_pem = $pk->export_key_pem('public');
#or
my $public_pem = $pk->export_key_pem('public_x509');
With parameter 'public' uses header and footer lines:
-----BEGIN DSA PUBLIC KEY------
-----END DSA PUBLIC KEY------
With parameter 'public_x509' uses header and footer lines:
-----BEGIN PUBLIC KEY------
-----END PUBLIC KEY------
Support for password protected PEM keys
my $private_pem = $pk->export_key_pem('private', $password);
#or
my $private_pem = $pk->export_key_pem('private', $password, $cipher);
# supported ciphers: 'DES-CBC'
# 'DES-EDE3-CBC'
# 'SEED-CBC'
# 'CAMELLIA-128-CBC'
# 'CAMELLIA-192-CBC'
# 'CAMELLIA-256-CBC'
# 'AES-128-CBC'
# 'AES-192-CBC'
# 'AES-256-CBC' (DEFAULT)
encrypt
Returns the ciphertext as a binary string.
DSA is usually used for signatures. This helper is available because
the underlying library exposes a DSA-based encryption primitive.
my $pk = Crypt::PK::DSA->new($pub_key_filename);
my $ct = $pk->encrypt($message);
#or
my $ct = $pk->encrypt($message, $hash_name);
# $hash_name .. [string] 'SHA1' (DEFAULT), 'SHA256' or any other hash supported by Crypt::Digest
decrypt
Returns the plaintext as a binary string.
my $pk = Crypt::PK::DSA->new($priv_key_filename);
my $pt = $pk->decrypt($ciphertext);
sign_message
Returns the signature as a binary string.
my $pk = Crypt::PK::DSA->new($priv_key_filename);
my $signature = $pk->sign_message($message);
#or
my $signature = $pk->sign_message($message, $hash_name);
# $hash_name .. [string] 'SHA1' (DEFAULT, INSECURE), 'SHA256' or any other hash supported by Crypt::Digest
BEWARE: The $hash_name default is 'SHA1' only for backward
compatibility. SHA-1 is vulnerable to practical collision attacks and
is not safe for signing messages whose content may be influenced by an
attacker. Always pass an explicit hash name such as 'SHA256'. The same
applies to "verify_message".
verify_message
Returns 1 if the signature is valid, 0 otherwise.
my $pk = Crypt::PK::DSA->new($pub_key_filename);
my $valid = $pk->verify_message($signature, $message);
#or
my $valid = $pk->verify_message($signature, $message, $hash_name);
# $hash_name .. [string] 'SHA1' (DEFAULT, INSECURE), 'SHA256' or any other hash supported by Crypt::Digest
sign_hash
Returns the signature as a binary string.
my $pk = Crypt::PK::DSA->new($priv_key_filename);
my $signature = $pk->sign_hash($message_hash);
verify_hash
Returns 1 if the signature is valid, 0 otherwise.
my $pk = Crypt::PK::DSA->new($pub_key_filename);
my $valid = $pk->verify_hash($signature, $message_hash);
is_private
my $rv = $pk->is_private;
# 1 .. private key loaded
# 0 .. public key loaded
# undef .. no key loaded
size
my $size = $pk->size;
# returns key size (length of the prime p) in bytes or undef if key not loaded
size_q
my $size = $pk->size_q;
# returns length of the prime q in bytes or undef if key not loaded
key2hash
Returns a hashref with the key components, or "undef" if no key is
loaded.
my $hash = $pk->key2hash;
# returns hash like this (or undef if no key loaded):
{
type => 1, # integer: 1 .. private, 0 .. public
size => 256, # integer: key size in bytes
# all the rest are hex strings
p => "AAF839A764E04D80824B79FA1F0496C093...", #prime modulus
q => "D05C4CB45F29D353442F1FEC43A6BE2BE8...", #prime divisor
g => "847E8896D12C9BF18FE283AE7AD58ED7F3...", #generator of a subgroup of order q in GF(p)
x => "6C801901AC74E2DC714D75A9F6969483CF...", #private key, random 0 < x < q
y => "8F7604D77FA62C7539562458A63C7611B7...", #public key, where y = g^x mod p
}
OpenSSL interoperability
### let's have:
# DSA private key in PEM format - dsakey.priv.pem
# DSA public key in PEM format - dsakey.pub.pem
# data file to be signed - input.data
Sign by OpenSSL, verify by Crypt::PK::DSA
Create signature (from commandline):
openssl dgst -sha256 -sign dsakey.priv.pem -out input.sha256-dsa.sig input.data
Verify signature (Perl code):
use Crypt::PK::DSA;
use Crypt::Digest 'digest_file';
use Crypt::Misc 'read_rawfile';
my $pkdsa = Crypt::PK::DSA->new("dsakey.pub.pem");
my $signature = read_rawfile("input.sha256-dsa.sig");
my $valid = $pkdsa->verify_hash($signature, digest_file("SHA256", "input.data"));
print $valid ? "SUCCESS" : "FAILURE";
Sign by Crypt::PK::DSA, verify by OpenSSL
Create signature (Perl code):
use Crypt::PK::DSA;
use Crypt::Digest 'digest_file';
use Crypt::Misc 'write_rawfile';
my $pkdsa = Crypt::PK::DSA->new("dsakey.priv.pem");
my $signature = $pkdsa->sign_hash(digest_file("SHA256", "input.data"));
write_rawfile("input.sha256-dsa.sig", $signature);
Verify signature (from commandline):
openssl dgst -sha256 -verify dsakey.pub.pem -signature input.sha256-dsa.sig input.data
Keys generated by Crypt::PK::DSA
Generate keys (Perl code):
use Crypt::PK::DSA;
use Crypt::Misc 'write_rawfile';
my $pkdsa = Crypt::PK::DSA->new;
$pkdsa->generate_key(20, 128);
write_rawfile("dsakey.pub.der", $pkdsa->export_key_der('public'));
write_rawfile("dsakey.priv.der", $pkdsa->export_key_der('private'));
write_rawfile("dsakey.pub.pem", $pkdsa->export_key_pem('public_x509'));
write_rawfile("dsakey.priv.pem", $pkdsa->export_key_pem('private'));
write_rawfile("dsakey-passwd.priv.pem", $pkdsa->export_key_pem('private', 'secret'));
Use keys by OpenSSL:
openssl dsa -in dsakey.priv.der -text -inform der
openssl dsa -in dsakey.priv.pem -text
openssl dsa -in dsakey-passwd.priv.pem -text -inform pem -passin pass:secret
openssl dsa -in dsakey.pub.der -pubin -text -inform der
openssl dsa -in dsakey.pub.pem -pubin -text
Keys generated by OpenSSL
Generate keys:
openssl dsaparam -genkey -out dsakey.priv.pem 1024
openssl dsa -in dsakey.priv.pem -out dsakey.priv.der -outform der
openssl dsa -in dsakey.priv.pem -out dsakey.pub.pem -pubout
openssl dsa -in dsakey.priv.pem -out dsakey.pub.der -outform der -pubout
openssl dsa -in dsakey.priv.pem -passout pass:secret -des3 -out dsakey-passwd.priv.pem
Load keys (Perl code):
use Crypt::PK::DSA;
my $pkdsa = Crypt::PK::DSA->new;
$pkdsa->import_key("dsakey.pub.der");
$pkdsa->import_key("dsakey.priv.der");
$pkdsa->import_key("dsakey.pub.pem");
$pkdsa->import_key("dsakey.priv.pem");
$pkdsa->import_key("dsakey-passwd.priv.pem", "secret");
SEE ALSO
o <https://en.wikipedia.org/wiki/Digital_Signature_Algorithm>
perl v5.34.3 2026-06-18 Crypt::PK::DSA(3)
cryptx 0.90.0 - Generated Sun Jun 21 15:28:49 CDT 2026